Maryland uses a mixed primary system. This means the power to decide who can vote in a primary is given to the parties. Parties decide who may vote in their primary election and generally close it to all voters except those registered with their party. (1)
Baltimore City is one of the four jurisdictions in Maryland where Democrats can only vote for Democrats and Republicans for Republicans in the primary election. Basically the Democratic primary winner becomes the de-facto Mayor. Independents are the largest new group of registrants in the city and little do they know that their votes do not count.
The Baltimore mayoral election is scheduled for November 8, 2016 along with the 2016 General Election.
Stephanie Rawlings-Blake, the incumbent mayor, announced she is not running for reelection. Due to the heavy Democratic Party leanings in Baltimore, winning the Democratic Party primary election is considered tantamount to election as mayor. Tantamount to election is a phrase in the United States to describe a situation in which one political party so dominates the demographics of a voting district, that the person winning the party nomination for a race (whether by primary or another method) will virtually be assured of winning the general election (2)